Syntax Magazine

SYNTAX

Serving

The Timex-Sinclair Family
Of Personal Computers

A PUBLICATION OF THE HARVARD GROUP

VOL. 3 NO. 8

ISSN 0273-2696

AUG., 1982

IN THIS ISSUE

4K Programs

Dice Roll . 21

8K Programs

Blast Effects . 5

Cardioid Plot . 21

Count . 17

Diagonal Lines . 17

Entrapment . 10

MC Screen Fill . 6

Sine Name . 3

Shifting Maze . 18

Spaces in REM . 8

String Functions . 18

Syntactic Sum Loader. 20
Book Review

Getting Acquainted with
Your ZX81f 3rd Ed. ..11
The Expandable ZX80

and ZX81 . 15

Classified Ads . 22

Dear Editor . 12

Hardware Projects
Preregulator and

Battery Backup . 4

Hardware Review

Memotech 64K Memopak.16
Machine Code Programming
CP Branching Tests... 8
Understanding the

Stack . 19

News, New Products. .1,2, 3
Printing Strings Faster. 5
Printing Bottom Line. ..15
Program Improvements .. .14
Shows and Exhibitions ... 3

Users' Groups . 3

Index of Advertisers

Byte-Back . 14

Memotech Corp . 9

Sof tsync . 11

Software Masters . 6

Syntax . 3

Zeta Software . 7,17

SYNTAX ZX80 UPDATES NAME

SYNTAX ZX80 now answers officially to
its abbreviated name, SYNTAX. The words
replacing "ZX80" on the banner reflect the
change in North America to the TS1000 compu¬
ters. They also emphasize our exclusive
coverage of all Timex-Sinclair computers. As
Timex introduces new computers, you'll find
them covered in SYNTAX.

VIDEO UPGRADE KITS FOR ZX80 IN US AGAIN

Once again ZX80 and MicroAce owners can
enjoy the flicker-free qualities of ZX81/
TSIOOOs. Kits, available in mid-August,
install inside computer case. Full kits
$32.50 plus $2.50 first class postage. Plans
$2.00 plus $.50 postage. Printed circuit
board with instructions $19.95 plus $1.25
postage. Orders are now being accepted by
Computer Engineering Services, PO Box 1222,
Show Low, AZ 85901, 602/537-7522. Specify
ZX80 or MicroAce when ordering.

SYNTAX QUARTERLY DEBUTS NOV. 82

SQ, The Syntax Quarterly, will be avail¬
able by subscription and on newsstands Nov.

1, 1982. (Ask your local computer store.)

The first issue will run about 64 pages
devoted to ZX and Timex-Sinclair computers.

Because of its quarterly publication, SQ
will not cover news. Instead, it will pro¬
vide longer programs, more extensive hardware
projects, and more in-depth tutorials than
the SYNTAX newsletter.

All SYNTAX subscribers will receive the
premiere issue of SQ free. Combined SYNTAX-
SQ subscriptions will cost $39 per year (12
issues of SYNTAX, 4 issues of SQ). SQ will
be available separately for $15 per year.

Address SQ program, project, or article
submissions to Syntax Quarterly, RD 2 Box
457, Harvard, MA 01451.

1

SYNTAX ERRORS: In the Apr. 82 logic
probe construction project, the LED
resistors should be 330 Ohms.

Numbers Held Inexactly in the
ZX81 (Jun.82) contains two errors.
On p.19, second paragraph, line 3,
the last number should be 205, not
204. On p.20, this line is missing
after line 11: .1 gives 125 76 204

204 205.

General Technology's phone no.
(Jul.82 p.22) is 401/273-2420.

NEWS, NEW PRODUCTS AND SERVICES

Help your first-sixth graders learn
at home. International Learning
Materials is producing child-tested
math, reading and grammar software
packages for ZX81s. Two math pack¬
ages, about $29.95 each, will be
available Sept. 1. Each contains 2
tapes (16 lessons each) and a work¬
book. Available from Gladstone
Electronics, 1736 Avenue Rd., Tor¬
onto, Ontario, Canada M5M 3Y7 and
Reston Publishing, 599 Adamsdale
Rd., N. Attleboro, MA 02760. For
more info, write Joseph Gladstone,
International Learning Materials,

95 Perivale Cres., Scarborough,
Ontario, Canada M1J 2C4.

In the offing: 16K EPROM and full-
sized keyboard from Memotech Corp.,
early this fall. EPROM (erasable
programmable read-only memory) lets
users with PROM-blowing capability
store programs directly in a read¬
only memory. EPROM will run about
$70 blank, according to Said Fateh
of Memotech. Big keyboard will
connect to computer's rear . so you
need no wiring inside the computer.
Price: under $80. Memotech Corp.,

7550 West Yale Ave., Suite 200,
Denver, CO 80227, 303/986-1516.

Instant Software needs programmers
to convert TRS-80 software to
TS1000 BASIC. If you're inter¬
ested, send your name, address, and
a description of your equipment to
Kevin Burton, Instant Software, 80
Pine St., Peterborough, NH 03458.

Sinclair's own software written by
Psion and ICL is available in the
US. Packages include business
($14.95-$17.95) , education ($12.95
each) and games ( $8.95-$13.95) .

Most programs require 16K RAM.
Sinclair Research, 3 Sinclair
Plaza, Nashua, NH 03061.

Get organized with a Consol-Kit
assembly from Hopper & Company.
Designed to fit Radio Shack's Mini-
sette 9 tape deck and RCA's Play¬
mate 9" TV, Consol-Kit assembles
into a complete computing center
with space for your ZX computer,

RAM pack and tapes. Full size
plans, $5; pre-cut kit $39.95 (7-
ply birch plywood). For more info,
send $1 to Hopper & Company, Inc.,
Box 689 Blue Hills Rd., Durham, CT
06422 or call 203/349-8424.

Gladstone's full-size portable
typewriter keyboards plug into ZX81
PC board. You get standard Sin¬
clair legends on removable keytops,
a full-size space bar and seven
extra keys, plus an edge card con¬
nector for adding extra memory.
Price: $109.95 Canadian, $85.00

US. Enclose it all in a black
anodized metal case, $29.95 Cana¬
dian, $25 US. Gladstone Elec¬
tronics, 1736 Avenue Rd., Toronto,
Ontario M5M 3Y7, 416/787-1448.

MX-Pac is designed to help you grow
from program user to program
writer. According to Bill Hoffman,
MX-Pac consists of 18 programs for
8K/1K on cassette with complete
listings and explanations.' Pro¬
grams range from simple to sophis¬
ticated and include Printout I, a
multi-level support and self¬
teaching guide. Price: $24.95.

Bill Hoffman, Robill Products, 555
Park Ave., Paterson, NJ 07504.

Dave Hallas tells us Programming
for Real Applications by Randle
Hurley, reviewed Jun.82, is $9.95
from Dilithium Press, PO Box 606,
Beaverton, OR 97075, 800/547-1842.

i

I

2

Data-assette introduces a whole
line of ZX hardware and software.

In addition to their ZX99 tape
controller and serial printer
interface, they offer: 16K, 32K
and 64K RAM packs (send your 16K
and get $15 off 64K); mini- and
full-size keyboards (full size with
repeat key); business, home and
game software (including a word
processor); computer cassettes,
storage racks, labels and repair
kits. Data-assette, 52 S. 3rd St.,
Oxford, PA 19363, 215/932-3626.

ADDENDUM TO CAI PRINTER REVIEW
(Jul.82): To use the CAI/O board

and Memotech's 64K RAM, first plug
the RAM into the computer. Then
plug the CAI/O board into the RAM.
Also note that if you use software
with imbedded keyboard printer com¬
mands, you will have to change each
command to the correct USR call.

USERS' GROUPS

To list your group, call
617/456-3661 or write SYNTAX, RD 2
Box 457, Harvard, MA 01451. To
find a group in your area, call or
send us an SASE and we'll send you
what information we have. — AZ

Seabrook/Lanham, MD: Lanham
Sinclair User's Group, Cora C.
Dickson, 9528 Elvis Ln., Lanham, MD
20706, 301/577-6645.

Manitoba, Canada: Sinclair Users'
Group, Box 777, Swan River,
Manitoba, ROL 1Z0

UPCOMING SHOWS AND EXHIBITIONS

The US Festival: Music festival
and technology exhibit including
professional and amateur hardware
and software producers. Sept 3-5,
1982, Glen Helen Regional Park, San
Bernardino County, CA

The Twin Cities Computer Show:

Sept 16-19, 1982, Minneapolis Audi¬
torium and Convention Hall.

Available from SYNTAX . . .

For computing beginners —

Crash Course in Microcomputers . $17.50

Covers hardware, machine language and
applications. Reviewed in SYNTAX, Oct. 1981.
Add $1.50 shipping.

For advanced hardware/software users —

Zilog’s Z80-Z80A CPU

Technical Manual . $7.50

Zilog’s Assembly Language

Programming Manual . $15.00

Add 5% for shipping.

Experiments in Artificial Intelligence

For Small Computers . $8.95

Giving your computer reasoning and
learning capabilities. Programs
translatable to Sinclair BASIC.

SYNTAX back issues available, $4 each.

Call or write for our group subscription discounts.

SYNTAX • RD 2 Box 457 • Harvard, MA 01451
617 / 456-3661

Gladstone Electronics' new US
address, effective 1 Aug 82: 1585

Kenmore Ave., Buffalo, NY 14217.

SINE NAME — 8K/1K

Print any string in the form
of a vertical sine wave. Type in
this program, RUN it, then enter a
string of up to 12 characters.

Along with letters, you can enter
graphics characters for neat
effects (for example, alternating
spaces and solid black squares for
an op-art design).

To run on an 8K ZX80, add:

37 PAUSE 30

Change SIN in line 20 to COS
for a cosine version.

Mark Freitas, Chelsea, Ml
5 INPUT

1@ FOR fi-0 TO 6.3 STEP .2
20 LET Y=SXN R
30 PRINT RT ai,

35 SCROLL
40 NEXT R
50 GOTO 1©

SYNTRCTIC SUM: 7555, ©K

3

TWO PROBLEM-SOLVING CIRCUITS — PREREGULATOR AND BATTERY BACKUP

Ed Buttenhoff's pre-regulator
circuit uses an LM340-8 regulator
(May82). While it works fine, that
regulator is not as commonly avail¬
able as LM340-5. Fig. 1 following
is a circuit that performs the same
function as Ed's Fig. 1 and uses a
garden-variety LM340-5 or 78L05 and
two resistors to provide the 8-volt
pre-regulation. You may replace
the 100 Ohm resistor with a 100 Ohm
trimpot in series with a 22 Ohm
resistor to make the output adjust¬
able; we recommend that you set the
regulator output at 7.5 volts,
which is plenty for operation while
allowing the lowest possible line
voltage (about 110 volts).

From
Sinclair
Power —
Supply —

-O

LM340T-5

22uF

24011

ioon

- O +

Output
to
ZX8 1

luF

-O —

Figure 1 — 8V Preregulator

Resistors are 1/4 W, 5% film

Fig. 2 shows a circuit to
provide battery backup for about
one hour. Seven Nickel-Cadmium AA
cells in series form the battery.

It is recharged directly from the
Sinclair power supply through R1 as
long as power is present. Diodes
D1 and D2 form a clamp which shuts
the battery off when input voltage
from the power supply is present
but instantly connects the battery
during a power interruption.

An optional SPST switch allows
you to reset the computer without
pulling the plug. We also suggest
additional filter capacitor (Cl) —

1000 uF or more. Also optional are
transistor Ql, resistors R2 and R3,
and LED1 which indicate that AC
power is present when the LED is
on. (This scheme is used instead
of an LED and resistor across the
input line as the battery would
discharge through R1 and the LED
with AC off and there is not enough
output voltage from the Sinclair
power supply to allow another diode
drop and still charge the battery
adequately.) Ql is a PNP silicon
transistor — 2N4443, 2N3906, or sim¬
ilar. R2 and R3 are 1/4 W, R1 is
1/2 W. There is even enough room
to install the entire circuit in¬
side the ZX81 case if you're adven¬
turous. This circuit is the same
as that used in the SYNCWARE BBU-1
battery backup unit.

Note that the circuit in Fig.

2 cannot successfully be followed
by the preregulator of Fig. 1
because the output voltage (taking
diode drop into account) is in the
vicinity of 8 volts — just enough to
operate the ZX81 directly.

Our BBU-2 battery system uses
10 NiCd cells of higher capacity
for longer running time, followed
by a preregulator for cool running
and improved glitch-rejection.

This scheme requires a new power
supply of about 16 volts; Sin¬
clair's doesn't put out enough
voltage to recharge the 12-volt
battery. Not only does this type
of system allow portable operation
and protect against power-down, it
also makes the ZX81 practically
immune to line glitches and noise.

Fred Nachbaur, Syncware Co.,

El Monte, CA

At SYNTAX we built the battery
backup unit to test. Operation is
just as described. Our unit fits
in a small box (Radio Shack 270-
233) which holds two, 4-cell
plastic battery holders (RS 270-
391). We rewired one holder to use

4

only 3 cells. You can use RS 23-
125 cells for the NiCd battery, but
they only provide 450 mAh and cost
more than $2 per cell.

If you'd rather not build your
own, you can buy these battery
packs from Syncware Co., 4825
Elrovia Ave., El Monte, CA 91732
for $39.50-$84.50. The schematic
shown is their commercial unit.
Patrick Spera called the BBU-2
"professional in appearance, per¬
formance and craftsmanship" in the
Sinclair Computers User's Group of
OK newsletter. — KO

o <-

U ft 3
G CO

■H

cn

WARNING: Do not leave battery pack

plugged into wall unless computer
is connected. Batteries will
overheat .

PRINTING STRINGS FASTER

While drawing some bar graphs
in the SLOW mode, the PRINT routine
was so slow I could actually see
each character appear. I tried
using the excellent string-handling
capability of the 8K ROM. The

difference was dramatic. Try both
of these in SLOW:

The slow way —

100 FOR 1=1 TO N

110 PRINT "X";

120 NEXT I
The fast way —

100 LET L$="XXXXX...X" (at least N
Xs)

110 PRINT L$( TO N)

Martin H. Irons, K2MI, Goshen NY

Choose a fairly large number to
substitute for N. If you have
enough memory, this method certain¬
ly speeds string printing. The
routine following demonstrates how
fast it can be. — AZ

BLAST EFFECTS ON ZX81

This simple subroutine simu¬
lates laser, cannon shots, and
other effects used in arcade-type
games. You can easily modify it
for your particular needs. Try
substituting different characters
in the strings or varying the num¬
ber of strings used. Line 210
sequentially overprints A$ through
F$ in a rapid and dramatically
effective manner. With a little
imagination, you can produce a
variety of startling "blasts".

Dan Tandberg, Albuquerque, NM

1 REM "BLR3T-
19 SLOU

30 LET
XXXXXXXX
4.0 LET
#******«•
5© LET

60 LET

XXXXXXXXXXXXXXXXXXX
*■£•**£■*■**■* **********

60 LET R = 1©

SB LET C=S _

10© PRINT AT R,C-5r^W„

-7 3 f* PRINT RT R + 3L .x C HI m

a©! IF INKEY $=”" 'THEN GOTO 300

SIS PRINT RT R •'

T R . C : C $ I RT RjUJ hT R .» P .• E # -* F! •
R,c; Fiji ‘

asa goto as© . _

jr Y NT P CT I C SUM: £24.4. t , SN

5

5..4..3..2..ZX81

Lift off your ZX81 with these
important books!

Machine Language made simple -

an introduction to Assembly Language programming for the
Sinclair ZX81 .

Understanding Your ZX81 -

understanding the monitor and help yourself to good machine
language programs.

Sinclair ZX81 ROM Disassembly Part A 0000H -0F54H -

An examination and notes on covering all except expression
evaluation.

Sinclair ZX81 ROM Disassembly Part B 0F55H-1DFFH -

An examination of all routines concerned with an evaluation of
expressions, and including an analysis of floating point
representation.

Explorers Guide to the ZX81 -

Goes on where the manual leaves off - a wealth of detailed
information on how to get the best out of your ZX81 but definitely not
for the beginner.

Use the Coupon below and we’ll rush your order by return.

QTY. (tick box)

MACHINE LANGUAGE MADE SIMPLE □ $19.95

UNDERSTANDING YOUR ZX81 ROM □ $19.95

EXPLORERS GUIDE TO THE ZX81 □ $19.95

ZX81 ROM DISASSEMBLY PART A □ $14.95

ZX81 ROM DISASSEMBLY PART B □ $14.95

| NAME _ □ SEND ME YOUR FREE CATALOG

| ADDRESS _

| CITY _ STATE _ ZIP _

ADD □ $1 .50/book UPS or □ 75c book 4th class mail or
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Software Masters, P.0. Box 1155, Evanston, Illinois 602 04

MACHINE CODE SCREEN FILL

This simple 16-byte machine
code program fills the screen with
any character. It executes faster
and takes up less space than the
BASIC program by Paul Qualls, Jr.,
in Jun.82 (p.20).

The MC routine is contained in
this REM statement:

l rem ySA . ®not $trb Drnd| tbb

\RNDTfiN

There are 16 keystrokes after REM.
For easy typing, follow this guide.
Finished result should look like
the line above:

1 REM Y inverseSPACE graphicT
graphic4 : inverseK tokenNOT $
tokenTAB inverseH tokenRND graphic5
tokenTAB graphicY tokenRND tokenTAN
Don't type any spaces. Spaces in
line 1 come from keywords (tokens).

Execute line 1 by entering
RAND USR 16514 in the FAST mode.
Almost instantly, the entire screen
blackens. The second keystroke
after REM is the fill character,
here inverse space. To change this
character, substitute another for
the inverse space, or POKE the new
character's code to address 16515
in the immediate mode (with no line
number). Be sure this REM line is
the first line in your program.

The assembly listing for this
routine (128 in location 16515 is
inverse space) follows next page.

If you'd rather POKE the decimal
values in, use a loader program:

1 REM (16 spaces)

2 FOR X=16514 TO 16529

3 INPUT I

4 POKE X,I

5 NEXT X

RUN, then input the numbers in the
assembly listing dec. column, hit¬
ting ENTER or NEWLINE after each.
After the last number press LIST
then ENTER or NEWLINE to see the
listing again. Line 1 now looks
like Dr. Miller's line 1. Delete
lines 2-5. Or use David Ornstein's
XFER hex loading program (Jun.82)
to load the hex numbers. — AZ

6

Loc.

Dec.

Hex

Opcode

Comment

16514

62

3E

LD A,N

;load code of fill character

16515

128

80

16516

6

06

LD B,04

;set LOOP1 counter for 4

iterations

16517

4

04

16518

14

0E

LOOP1 : LD C,B0

;set LOOP2 counter for 176

iterations

16519

176

B0

16520

215

D7

LOOP 2 : rst 10

;character printing routine

16521

13

0D

DEC C

; reduce LOOP2 counter by 1

16522

194

C2

JPNZ ,LOOP2 ; if C=0, go to LOOP2

16523

136

88

16524

64

40

16525

5

05

DEC B

; reduce LOOP1 counter by 1

16526

194

C2

JPNZ ,LOOPl ; if B=0, go to LOOP1

16527

134

86

16528

64

40

16529

201

C9

ret

;B=0, return to BASIC

Using a loop within another loop, this ML program executes the
character printing routine exactly 704 times (4*176=704), which fills
the screen. By POKEing smaller values into registers B and C, you can
fill as much of the screen as you wish.

Harold Miller, Clarkesville , GA

ZX81 OWNERS with 16K RAM!
IT'S READY— ARE YOU?

,o£L H2i*r>

$14.95 +
2.50 S&H

If so. .you get:

*24-row/full-screen displays
*Nearly 2K of machine code
for FAST real-time graphics
*A 4K Star Atlas as the moving
backdrop during enemy engagements

*9-each fuel and skill levels that
are interlocked for more "reality"

*4 ways to lose — no fuel, no oxygen,
no gun power, or no shields. 1 way
to win — destroy ALL enemy craft.

*An enemy data generator imbedded in
the run as part of the "action"
*"Blink"-less pauses in BASIC
*Sti ck-on/peel-off custom keys
*In-depth booklet explaining both
the "game" and the program
*Shipped on a certified cassette
1 copy each side

16K Programs for either ZX80-8K or ZX81

*PLANE FRAME-model 1 ing for engineers
*FUNDAMENTAL ANALYSIS-for stocks investors
*P0LSAT & GEOSAT-space age Ham Radio uses
*MATH PAK-Routines & Fit, Variance Analyzer,
Statistics, and RPN Calculator
__TA *E.S.P.-test your precognition

ZrTM *Many others plus 6 IK 6-paks

SOFTWARE^Jr including Machine Code

WRITE for free catalog. (In
Europe, send U$1 bill or DM2 stamp:
DELTASOFT/Osterfeldstr. 79D/D-2000 Hamburg 54 GER)

CO

o

kO

cr>

C\J

o

oo

C\J •
C\J CD
LO i —
OO «—

•r—

X >

o c

CO CD
CD
O

D_ CD

rplail coupon or copy with payment to:

| ZETA Software/PO Box 3522/Greenvi lie, SC 29608

DCheck □.

I Enclosed is $ _

| for _ copy(ies) of SCOUT FIGHTER ZX81 16K

plus $2,50 S&H for the order.

NAME

ADDRESS

I

CITY /STATE/ZIP _

I Please allow 4 weeks if paid by check.

MACHINE CODE — CP BRANCHING TESTS

SPACES IN REM STATEMENTS

CPs are 1-3 byte codes that
compare two numbers. More exactly,
they subtract the number you are
looking for from what has been
loaded into the Accumulator. The
general method of using CPs is to
set up a loop that will "peek" into
a block of addresses serially, or
one after another.

For instance, suppose you have
a block of data in REM addresses
and you want to return to BASIC at
the last piece of data:

1. Choose a number that is not
valid data, say 23, and store it in
the last data address in the block.

2. Initialize a register pair as a
"data pointer" with an INCrement
instruction. Load A with the con¬
tents of the address pointed to.

(LD A, (BC) for example, where BC
holds the current data address and
is stored on the stack.)

3. Compare the new data to "23"
(CPn, where n=23).

4. If the data is. 23, the Z flag
is set for a test so you can branch
(either to BASIC or to reset the
pointer). If the data is not 23, A
still contains valid data (only the
Flags are affected) , the branch-
test (RET Z, JR Z, etc.) fails, and
the data can be processed.

CPs are simple to use if you
understand two things: A must be
loaded with "unknown" data from an
address, and you must follow the CP
with a test-and-branch depending on
which Flag you test (JR C, CALL PO,
nn, RET NZ, JP M,nn, for example).

In addition to CPs, the Z80
also has a few instructions that
actively search and test data auto¬
matically. With these, however,
you must load-initialize HL with
the data address and load BC with
the number of addresses to search
(iterations of the automatic loop).

Next: TESTING BITS FOR BRANCHING

Jon Bobst, Zeta Software, PO Box
3522, Greenville, SC 29608-3522

If you put your machine code
in large REM statements, you need
not laboriously type in spaces or
digits. This 8K/16K program pro¬
duces a REM statement containing up
to 14991 full stops. You choose
the number you want at line 40.

Delete lines 10-130 after
running. You can change the line
number for the REM statement by
editing line 200 after your REM
line is created. If the line is
too big to edit, POKE 16510,1 works
after you delete lines 10-130.

Lines 20 and 30 are fool-proofing;

I would not advise deleting them
until you are happy with your REM
statement .

This routine simply builds up
the REM line one byte at a time,
calling the ROM routine that makes
one space and moves all the point¬
ers up each time. It's quicker to
make all the spaces at once, but a
bit more complicated to program.
Using this method, a 500-byte REM
line takes less than 20 seconds.

If you prefer digits 1234...,
change line 100 to:

100 POKE D+I,I-10*INT (l/10)+28

Hex code in line 10 reads:

ID IE 2A 82 40 CD 9B 09 C9
The keystrokes in line 10 after 10
REM are:

numberl number2 letterE graphic-
shiftw tokenRND tokenLN inverse
period graphicshif tD tokenTAN
Don't type any spaces.

Frank O'Hara, Surbiton, Surrey, UK

10 REM 12
£0 PRINT
GOTO 40”

SO STOP
4© INPUT N
5© L.ET D=PEEK
6397-2

6© FOR 1=1 TO N

NDLN UsssThN
NTER £00 REM; THEN

16396 +256 *PEEK 1

70 POKE 16515, XNT « (0+1) ^256)
60 POKE 16514 , D + 1 -256 *PEEK 165
15

90 RRND U5R 16516
100 POKE D+X,27
1 1® WFVT T

12© POKE D— 1,INT ( (N+2i ^256)

130 POKE D— 2 , N -1-2 -256 sPEEK CD-I)
SYNTACTIC SUM: 17705, SK

8

Explore the excellence of your ZX81 with a

9PBK64H memory extension for $179.95

Give your diminishing memory more byte.

MEMOPAK 64K RAM $179.95

The Sinclair ZX81 has revolutionized
home computing. The MEMOPAK 64K
RAM extends the memory of ZX81 by a
further 56K to a full 64K. It is neither
switched nor paged and is Directly
Addressable. The unit is user trans¬
parent and accepts such basic com¬
mands as 10 DIM A (9000). It plugs
directly into the back of ZX81 and does
not inhibit the use of the printer or other
add-on units. There is no need for an
additional power supply or leads.

Description of memory

0-8 K . . . Sinclair ROM
8-16K . . . This section of memory
switches in or out in 4K blocks to leave
space for memory mapping, holds its
contents during cassette loads, allows
communication between programs, and
can be used to run assembly language
routines.

16-32K . . . This area can be used for
basic programs and assembly language
routines.

32-64 K . . . 32 K of RAM memory for
basic variables and large arrays. With
the MEMOPAK 64K extension the ZX81
is transformed into a powerful com¬
puter, suitable for business, leisure and
educational use, at a fraction of the cost
of comparable systems.

ncnoitCn

Memory Extention Specialists

Memotech Corporation
7550 West Yale Ave., Suite 200
Denver, Colorado 80227

Ph.(303) 986-1516

MEMOPAK 16K RAM $59.95

With the addition of MEMOPAK 16K,
your ZX81 will have a full 16K of Di¬
rectly Addressable RAM. It is neither
switched nor paged and enables you to
execute longer and more sophisticated
programs and to hold an extended data
base.

The 16K and 64K Memopaks come in
attractive, custom-designed and engi¬
neered cases which fit snugly on to the
back of the ZX81 giving a firm connec¬
tion.

Free service on your MEMOPAK

Within the first six months, should any¬
thing go wrong with your MEMOPAK,
return it to us and we will repair or
replace it free of charge.

Try MEMOPAK with no obligation

You can use our MEMOPAK in your
home without obligation. After 10 days
if you are not completely satisfied,
simply return it for a full refund.

Coming soon .

A complete range of ZX81 plug-in
peripherals:

MEMOTECH Hi-Res Graphics
MEMOTECH Digitising Tablets
RS232 Interface
Centronic Interface and
Software Drivers

All these products are designed to fit
“piggy-back” fashion on to each other
and use the ZX81 power supply.

Further information forthcoming.

Memotech Corp. 7550 W. Yale Ave. Suite 220 Denver, Colo. 802271

Yes! I would like to try the Memopak. I understand that if I’m not complete satisfied,

I can return it in 10 days for a full refund. Price + Qty Amount

□ Check

□ Visa

□ MC

Act . No. [

Name _

Street

Memopak 64k RAM

$ 179.95

Memopak 16k RAM

$ 59.95

Shipping and Handling

$ 4.95

$ 4.95

t U.S. Dollars

ENTRAPMENT — 8K/16K

This game pits you against
your 8K computer. The playing
field is a rectangle with two diff¬
erent starting points. The compu¬
ter controls the + character and
you control the inverse *. You try
to maneuver the computer's string
of plusses into a box the leading
plus cannot get out of. The compu¬
ter will not hit the boundary,
itself, or your string of asterisks
as long as the lead plus can move
in a direction that is not occu¬
pied. You win when the computer is
unable to find a clear direction.
You lose if your string is trapped.

To control your string, use
these four keys:

K right
J left
M down
I up

(See Jun.82 p.10 for info on adding
a joystick to your ZX81. — AZ) If
you do not push a key for movement,
the computer will continue your
string to the right. So be careful
not to let your lead asterisk
double back on itself. Changing
line 266 to GOTO 530, 550 or 490
moves the asterisk in another dir¬
ection if nothing is pressed.

Each symbol is mapped into
memory by the POKE command at its
corresponding coordinates. B in
line 60 is a random memory location
for storing information.

The program runs again automa¬
tically. To exit, press BREAK.

Wayne C. DeJulia, Ozone Park, NY

5® CLERR
55 CLS

6© LET E =30300
©9 FRST

70 FOR i_=a TO 19

71 FOR H=2 TO 3®

7a POKE B+L*4-0+M . CODE t" ’*)

73 NEXT M
74. NEXT L
S© ROND

11© FOR H = 1 TO 31
IS© PRINT RT 21,N; ‘ jp”

130 PRINT RT 1 „N;

14.0 POKE B+21*4-0+N .CODE ( S
15© POKE B+l*4-0+N .CODE t ” J*7* j
16® NEXT N

170 FOR N=1 TO 21
IS® PRINT RT N . 1 ; "J*"

190 PRINT RT N . 31; "J*"

200 POKE B+N*4.S + l,CODE { ” Ji» j
210 POKE B+N*4-3+31 ,, CODE < •• J»“ )
220 NEXT N ^

225 SLOW

230 LET R = INT £ RNE> * 16+3)

2^0 LET C = INT iRND*2S+2i
2|0 PRINT RT fi,C; ,,4."

P2^ErvB+f:i*',t®+CJ.COE>E C»+»j

LET D-INT (RNDH74.2)
iS? ‘E = IK1T £RlMD*Q6+a)

RR1NT RT D ^ E :

255 POKE B+D*ia+E,CODE (»■■■!

256 LET M S = INKEYS ®

118 i! ni-'-T- TSPK goto bio

111 ll ™§H §§T§ III

111 ioTO*SiB THEN GOTO *»•

27© LET G=C + 1

"?aTHFWP^Tn iB + 0*4B+C)

.-,2,.,TNEN GOT O 2Q0
273 PRINT RT fi p •»«.«»

121 88?g |si*2^.S0[>E
1§1 tIT g=g=|

^STHENP|oTO ^li©**®*0* <>CODE
310 PRINT RT RJ0j>*+**

330 §8?g gig CODE

111 tp s=gti

"f4‘THFKiPrnTn <3+0*4.04-0

II! SgSg !gg*40+C.CODE
LET ffs-a.i
•*-83 LtT R =R — 1

(£0®^ <R*4-0) +o

410 pbint_rtIr.o®+**

& 4* £ fi £4>0 j +r* rnnp c ** * «
4-30 GOTO SBS ( 1 + ’

4 *t>0 OLS

ill PAUSE ila10'10* ,,YOU win**
4-65 GOTO 5©

F9© LET E=E-1

”?ST5£K.P^f^« £B+D*4.0+E>
-l^THEN GOTO 70©

imo O . E: !,E5"

Srai £®KE B+D*4-©+E . CODE
5©3 GOTO 27©

51© LET E=E+i

PEEK C 3+0*4.© +E) <

) THfcN GuTO 7©©

POKE B +0*4.0 +E. CODE

522 PRINT RT D . Ea "B"

523 GOTO 27©

S3© LET 0=0-1

"l'0THENPloTO<lj0*iO<'E’ <>CODE

IS! PRXNTBRT*D^f.'B°DE ‘"B"“

54.7 GOTO 27© ‘ *

55© LET 0=0+1

5S8 IF PEEK { B +0 *4.0 +E 1 < >COOE
) THEN GOTO 700
565 POKE B+O*4-0+E . CODE i "B" J
570 PRINT RT O „ Ea "H" **

5a75 GOTO 273
70S CLS

705 PRINT fif 10. 12a "YOU
715 PRUSE 1©©

720 GOTO 50

SYNTRCTIC SUM: 4-2089 , ©K

< s-CODE C

t“+")

<“+")

< >COOE
t"+")

< >COD£

e >CODE

C "fS" )

>COOE

t

‘1

LOSE1

io

BOOK REVIEW

Title: Getting Acquainted with

Your ZX81 (3rd. Ed.)
Author: Tim Hartnell

From: Creative Computing Press

Price: $8.95 paperback

This British book is a good
way to move beyond the ZX81 manual
if you're new to computers.

Between fascinating graphic display
programs (Star Map, Micro Mouse)
and challenging games (Space Boy,
Alien Imploders) is a reasonable
amount of explanatory text.

Hartnell is, from time to
time, very good at setting problems
for his readers to work out. This
is essential in any teaching text,
and it is good to find it here.

Significant discussion is
given to saving memory by refining
programs (with some examples), RND,
SCROLL, program-writing sugges¬
tions, using arrays and a fair
amount more. Finally, after some
work programming and numbering a
checker board for efficient use in
programs is a version of checkers.

The last ten pages may be as
much help as all the rest. Hart¬
nell discusses how to change pro¬
grams from 4K to 8K ROM, gives a
set of specifications, a table to
convert system variables from old
to new ROM, and a listing of the
character set, ending with direc¬
tions for replacing a 4K ROM with
an 8K one.

There are minor problems with
the book beyond the British names.
It is occasionally hard to read
programs correctly; at least once I
read 0 for zero and F for E. Using
report codes and some detective
work, you can figure these out.

Although I haven't run all of
the more than 80 programs, exten¬
sive sampling and reading all the
text showed this to be a very help¬
ful book for anyone just getting
into the ZX81.

Ronald H. Miller, Murrysville, PA

SOFTSY1XC, IXC. #*.*/*.

ZX81— TSIOOO—

BACKGAMMON - S/

BACKGAMMON is a 3,000 year old game of
chance and skill between two people -- or in this
case between a person and a computer. This high
quality ZX81 Backgammon program uses fast and
efficient machine code to choose its moves and
includes a detailed playing board and rolling dice.

A comparatively modern addition to the game,
which is included in this program, is the doubling
cube giving the game an extra dimension and
enchancing the opportunity of using skill rather
than just luck to defeat your opponent.

Side “B” of the cassette contains a bonus
program -- full screen rolling dice which can be
used to play any dice game. The program uses the
random number generator so the rolling is
guaranteed to be completely random. Handy when
playing with opponents you suspect of "loading”

the dice.

16K $14.95

PLUS MANY MORE PROGRAMSI

kWRITE FOR FREE CATALOG

-AND FREE LISTING ,

copies of BACKGMN

Please send me _

@ $14.95 each.

Please add $1.50 shipping & handling
New York residents add sales tax.

I enclose _ _ _ .

SEND CHECK OR MONEY ORDER TO

SOFTSYNC, INC.

TO Box 480, Murray Hill Staton, New York, N Y 10156 (212) 685-2080

I Foreign orders must be paid by International Money Order or
foreign draft m U.S. Dollars drawn on a New York bank

NAME _

STATE/ZIP.

11

DEAR EDITOR:

Since adding a Sinclair 16K
RAM expansion, a horizontal bar
travels constantly up my screen.

The IK computer doesn't do this.

I have tried three different
TV sets with the same results.

What can I can do to eliminate
this horizontal bar? Keeping both
the TV contrast & brightness con¬
trol at a minimum diminishes this
effect but doesn't eliminate it.

I suspect that the computer
and the 16K pack overload the power
supply but I cannot be sure. I
have the 650 MA power supply.

Luis A. Roman, Ponce, PR

That's right — your power supply has
excessive ripple. Sam Porter sug¬
gests you increase C3 in the compu¬
ter from 22uF to 220uF (Apr. 82
p.18), but see the following letter
and answer for alternatives. — KO

Sam Porter's fix for charger
ripple (April 82) treats the symp¬
tom, not the disease. Horizontal
"hum" bars on the screen do result
from a weak charger, but the power
supply is weak because a component
has failed. The most likely cul¬
prit is one of the two diodes
soldered to the transformer wind¬
ings inside the plastic case. If
one diode opened, supply capacity
drops by 1/2 and more hum results.
Adding capacitance reduces the hum
to a workable level, but replacing
the diode is a better fix.

To get inside the sealed plas¬
tic case, use a sharp knife to cut
the plastic welds along the crack
between the case top and bottom.

The power supply already has a
1000 uf, 16V cap in it.

William Bosley, Valparaiso, FL

Chargers can also develop excess
ripple if the transformer is badly
wound. Voltages would be within
specs, but ripple would be high.

especially after warmup. You can¬
not easily repair bad windings, so
get a new unit. ZX80/1 owners
should write to Sinclair Research,

1 Sinclair Plaza, Nashua, NH 03061.
Use this address for all parts,
manuals, and ROM upgrades. — KO

If you added a big keyboard
and need to label 8K functions on
the keys, here's a suggestion from
Chuck Ludinisky of Chelmsford, MA.
Find a Sinclair ad in the computer
magazines; color in Kilobaud or
Byte, b/w in SYNTAX. Cut out the
keyboard picture and glue the
labels to your keytops with house¬
hold (airplane) glue. Cover with
tape or clear nail polish. The
labels are small, but readable.

Cliff Danielson, Chelmsford, MA

Sometimes pressing on the top
of my ZX81 case in certain areas
causes a crash. Static from my
hand isn't causing it. Do you know
what might be causing the problem
and what the solution is?

Hugh B. Amber, Mississauga, Ont.

Check the insulation between
ground strap & circuit board —
sometimes the tape punctures.
Cracked traces & solder joints give
similar symptoms. — KO

In Apr. 82, Don Shank, Palo
Alto, CA, wrote about problems with
his ZX81's power jack connection.

I had the same problem with my
power connection. (Sinclair should
fix this!) I wouldn't put up with
this problem nor would I put my
computer on the shelf. Replacing
the existing power plug with an RCA
type plug would solve this problem,
so I got the necessary parts from a
local electronics store and in¬
stalled them. Problem solved.

I am by no means an electronic
repairman but this plug can be
installed with a little imagination
and care. You need only a screw-

12

driver, a relatively inexpensive
soldering iron and about 2" of 16
to 18 gauge wire.

I hope Mr. Shank reads this
letter and takes his ZX81 back off
the shelf. He's missing a lot of
pleasure and an enjoyable teaching
aid for himself and his family.

David L. Isabel, Farmington, MO

I am just starting on the ZX81
and am looking for info:

1) Where to get parts to build
add-on RAM

2) Switch to color

3) Printer interface

4) List of owners in my area
(especially amateur radio operators
& electronics builders, computer
technicians)

James R. Copeland, Crozet, VA

Check electronics surplus houses
for inexpensive parts for hardware
projects. They often advertise in
the back of computer magazines like
Bvte. We have bought from BNF in
Peabody, MA, and John J. Meshna in
Lynn, MA.

Several people are working on
color boards for ZX81s. Watch
SYNTAX for details.

Printer interfaces with ASCII
conversion are available from Byte-
Back, Rt. 3, Box 147, Brodie Rd.,
Leesville, SC 29070? Data-assette,
52 S. 3rd St., Oxford, PA 19363;
and Memotech Corp., 7550 W. Yale
Ave., Suite 200, Denver, CO 80227.

To reach amateur radio users,
contact Marty Irons, K2MI, 46 Magic
Circle Dr., Goshen, NY. He runs a
free newsletter only for amateur
radio people with ZX81s. To find
local ZX users groups, see p.3. — AZ

My problem is that prepared
tapes LOAD satisfactorily; however
tapes SAVED from the computer do
not LOAD. The audio signal from
the tape is much weaker than the
prepared tapes (obviously what is
going out isn't strong enough).

The output from IC1 pin 16
exits via R29 (1M) and C12 (47pfd)
to MIC jack with R27 (IK) and Cll
(47nfd) to 0 volt bus.

Is there any obvious reason
why I cannot SAVE programs? Should
I disconnect R30?

A.R. Newhouse, Potomac, MD

Do not disconnect R30; it creates
the US TV scan and plays no role in
SAVE and LOAD. Try a borrowed tape
recorder, and use a short (C-30 or
smaller) tape. Next, check the
component values or substitute
others, and inspect the solder
joints and printed circuit traces.
Measure the output from the MIC
jack on your computer — you should
get 1-5 millivolts.

If you find no problem, we
recommend you exchange the unit or
send it for repair. — KO

I think I understand "phantom
memory" (addresses above 37767),
but I don't understand why some 8K
ROM code references locations in
the phantom memory. For example,
there is a CALL PO, 58085 (hex E2E5)
at 171 (hex 00AC) and a JP PO, 57310
(hex DFDE) at 180 (hex 00B4). Or
is my disassembly all wet? Simi¬
larly, more appear to be many ref¬
erences to locations between 8192
and 16383 (hex 2000 to 3FFF) . I
can accept this more readily but
still have some trouble with it.

Why don't I have 17K of RAM
with my 16K RAM add-on?

James H. Canfield, Dayton, OH

Addresses 00AC and 00B4 contain
text or tabulated values, not com¬
mands. Locations 007E to 01FB
contain the key tables. Unless you
like doing your own disassembly,
you can use Ian Logan's, available
direct from Ian in England or from
several North American suppliers.

Adding 16K external memory
disables the internal IK that comes
with the ZX80/81. — KO

13

PROGRAM IMPROVEMENTS

Grandson of Big Characters (Jul.82)
Here is a shorter version of Grand¬
son of Big Characters which allows
27 4x-size characters on a IK mach¬
ine. Input them one at a time.

Paul Ezra, San Diego, CA

2 LET <3*4-3
4- INPUT

6 FOR B*1 TO LEN R$

3 FOR C=® TO 7

2® LET D=PEEK (7660+CODE R$ <B>

25 FOR F=© TO 7
3® LET E=2** < 7 — F .>

35 IF D>*E THEN PLOT 8*<B-1}*F

» G"~C

4-0 IF D>=E THEN LET D=D-E

4-5 NEXT F

5® NEXT C-

55 NEXT B

6© LET G=G-8

65 GOTO 4-

5YNTRCTIC SUM: 14-634- , SK

BASIC Line Renumbering (Jun.82)

This modification provides more
flexibility and often negates the
need to change GOSUBs and GOTOs.
Because it lets you specify the
last program line to renumber, you
can retain subroutine starting ad¬
dresses .

Use this program the same way
as the original: type it in, SAVE
it, then reload before typing in a
new program. Call the renumber
program by entering GOTO 9980 in
the immediate mode. To exit early,
enter DELETE then STOP.

You can learn a lot about how
the computer handles programs by
manipulating program lines or giv¬
ing several lines the same number
(increment by 0). Try this:

50 SLOW

40 PRINT AT 21,11; "GOODBYE"

30 FOR X=1 TO 22
20 SCROLL
10 NEXT X

It runs fine if entered using nor¬
mal (low to high) line numbers and
renumbered with increment -10.
(Editing or adding new lines can be
a little tricky, though).

William Bosley, Valparaiso, FL

64K MEMORY
M-64 $119.9£t

129.95 WIRED & TESTED
IN STOCK. SAME DAY SHIPMENT
All standard features included, plus lower 8K
of RAM can be disabled in 2K segments to I

allow PROM or peripherals to be added.

EXPAND YOUR 16K SYSTEM

$59,951

If you have a Sinclair 16K RAM module and need

I more memory, expand it to 32K and beyond by using
BYTE-BACK M-16 MEMORY MODULES.

You can’t connect two Sinclair 16K RAM modules together,

I but you can connect one Sinclair 16 K and one or more BYTE-
BACK 16K modules to get all the memory you need.

THOUSANDS IN USE WITH PROVEN RELIABILITY

M-16 $59 -95 Kit. $69.95 wired and tested.

IN STOCK. SAME DAY SHIPMENT

BB-1 Control Module, with 8 relays, 8 leds
& 8 inputs. $59 Kit. $69 wire and tested.
IN STOCK! SAME DAY SHIPMENT

[modem with RS232 Port. $99.9K1t $Tte9s5teWd'.re

90-Day Warranty On All Modules.
10-Day Return Priviledge
ORDER PHONE 803-532-5812

Add $4.95 shipping & handling to ail orders.

BYTE-BACK CO. CHECKS

Rt. 3 Box 147 Brodie Rd.

LEESVILLE, SOUTH CAROLINA 29070 ■

89

S970 STOP
9971 LET R =16509
3973 INPUT S
■39373 PRINT S

3374. LET L=2S8*PEEK R+PEEK <R + 1>

3375 IF L sS THEN RETURN

3S7S IF L> =937© THEN GOTO 9373

9977 LEi R =R 4-4- -h PEEK (fl-4-21 +256*PE
EK (R+3)

9978 GOTO 3374-

9979 PRINT S; "NOT FOUND"

5222«£RSNT "crst line to be renu

HBEREDs ;

9981 GOSUB 9971
3982 LET RE *0+3

"1ST LINE TO BE renuk

9964- GOSUB 9971

9985 PRINT "1ST NEW LINE NUMBER*

9986 INPUT N

9987 PRINT N , " INCREMENT LINES BY

9988 INPUT I

9989 PRINT I

9990 IF R > RE THEN GOTO 9997

9991 IF N > 9959 THEN GOTO 9999

9992 POKE R , INT (N/&5B)

9993 POKE CR + l) .. N -256 if INT CN/S5&

9994- LET R=R+4-+PEEK tR+2) +256*FE
EK £R+3)

3995 LET N*N+I

3996 GOTO 999©

HU gRJNT * * "RENUMBER COMPLETE"
# /"CRNT COMPLETE. LIN
SYNTACTIC ’ SUM: 39756, SK

i

14

BOOK REVIEW

Powers of Negative Numbers
The formula for powers of negative
numbers that William Tracy attri¬
butes to Sinclair (Jun.82 p.12)
contains three mistakes. Line 10
of the program following corrects
these. The program also shows some
powers of -2. I have checked the
formula for positive numbers and
zero also. Zero to a negative
power overflows, as it should.

Frank O'Hara, Surbiton, Surrey, UK

2 LET A=-2
5 FOR B=-5 TO 16
10 PRINT ABS A**B* (1-(B-2*INT
(B/2) ) * (1-SGN A) ) ,

20 NEXT B

PRINTING ON THE BOTTOM LINE — 8K

According to Sinclair's pro¬
gramming manual, you cannot PRINT
on the bottom two screen lines.

This is not quite true. Here are
two different ways to PRINT where
you aren't supposed to.

1. One way:

10 LET L=USR 2591
20 PRINT "THE BOTTOM LINE"

30 PAUSE 1000

USR 2591 is a routine in the 8K ROM
that clears the bottom part of the
screen and is then effectively
PRINT AT 23,0;. This method is
crash-proof, but AT and TAB still
won't work at the bottom.

2. Another way:

10 POKE 16418,0

20 PRINT AT 2 3, 7; "THE BOTTOM L
INE"

30 FOR N=0 TO 23
40 PRINT AT N,0;N
50 NEXT N
60 POKE 16418,12
70 PAUSE 1000

You can now PRINT to the entire
screen, even using AT and TAB. Be
careful — if you INPUT while address
16418 (DF SZ) is less than 2, the
computer crashes. PLOT still
starts two lines above the bottom.

Jason Harper, Sylvester, TX

1

Title:

The Expandable ZX80 and

ZX81

By:

John F. Jarrett

From:

Computer Engineering
Services, The Jarrett
Company, PO Box 1222, Show
Low, AZ 85901, 602/537-7522

Price:

$9.95 + 1.25 shipping

If you are unsure about which
is the business end of a soldering
iron, then pass this book by. But
for the dyed-in-the-wool hobbyist,
it is a must.

Mr. Jarrett offers seven docu¬
mented projects and several ideas
for additional projects. The proj¬
ects include two memory expansions,
two different sound generators, a 5
amp power supply, a lamp/motor
controller, and a Digitalker (tm)
so your computer can talk to you!
All projects come fairly well docu¬
mented, with parts listings,
photos, and schematics. The author
suggests you wirewrap most of the
projects. I agree, unless you have
some skill at designing and making
your own printed circuit cards.

There are some things I don't
enjoy about this book. Mr. Jarrett
ignored both his large keyboard and
his enclosure for his expanded
ZX80. I feel these are important,
as there is no sense to making the
projects if you don't have a place
to put them! Also, while Mr.
Jarrett did include a parts list
for every project, he did not al¬
ways provide stock numbers* Per¬
haps he didn't wish to favor any
one company.

On the whole, I liked the book
and its projects. I feel the 8x11"
softcover is well worth the $9.95
price tag. I will most likely
construct all the projects, as cash
flow allows. Again, this book is a
must for builders who wish to make
the most of their Sinclair ZX80 or
ZX81 computer.

Patrick M. Spera, Tinker AFB, OK

HARDWARE REVIEW

Product: Memotech 64K Memopak

From: Memotech Corp., 7550 W.

Yale Ave., Suite 200,
Denver, CO 80227,
303/986-1516.

Price: $179.95 + $4.95 shipping

My 64K Memopak arrived within
three weeks of mailing my check to
Memotech. The module plugs direct¬
ly into the Sinclair port straight
out of the box, with a duplicate
port exposed on the back for con¬
necting the printer. It is com¬
pletely self-contained and requires
no external power supply. Since
the case is as wide as the compu¬
ter, Memotech provides double-sided
foam tape to secure the unsupported
end to the Sinclair. With the
tape, the Memopak is much less
susceptible to jarring and glitches
than the Sinclair module.

The instructions are easy to
understand and include an explana¬
tion of the 4 tiny switches acces¬
sible through the back panel. They
switch in or out 4K-blocks of mem¬
ory between 0000 and 16383 and come
preset to disable the first 8K of
memory (corresponding to the 8K
ROM). Thus you really have 56K of
usable RAM. Even though the first
8K is not available, it is imple¬
mented in hardware "for future
developments." You can only use
the second 8K for machine language
programs, and it is safe from NEW.
The next 16K works just like Sin¬
clair's module. To tell the system
that there is yet another 32K above
this area, you must POKE RAMTOP to
65535. Although BASIC listings
cannot extend into the top 32K,
they can now occupy almost the
entire 16K area below because all
program data and the stacks are
relocated. Refer to the ZX81 man¬
ual, p.128; everything above the
line marked VARS is moved to the
top 32K so the BASIC listing can be
up to about 15K long.

Operation of the Memopak is

quite satisfactory. Subjectively,

I got 5% more TV interference than
with the 16K module. This looks
like faint moire patterns, but
never so severe as to be obtrusive.
The screen clears quickly when
things warm up, and plugging in the
cassette recorder seems to help!
There is no overheating or evidence
of unreliability. SAVE and LOAD
work normally, and tapes made with
the 16K also LOAD fine. Should you
want to expand a data array on a
16K tape, you must re-enter your
old data manually.

The unit comes with a 6-month
guarantee, not 90 days.

ZX80 users can connect the
Memopak to their machines, but the
computer must be modified: change
one connection and add a resistor.

The Memopak is undoubtedly the
ultimate memory expansion for the
Sinclair. Try DIM A(9500)!

Gene Alvarez, Oviedo, FL

Daren Lyons, Swartz Creek, MI, also
wrote about his 64K Memopak. He
agreed with Gene, except that his
ZX81 power pack tends to overheat
with the Memopak attached. He
added, "The reaction time is
slowed. When the pack is attached,
things get real slow. Commands
used outside of programs, and some
used inside, get slow enough to
watch the screen clear line by
line, and RUN, LIST, etc., take
forever to make any action known to
the user."

Our Memopack works well and
fits snugly on the ZX81. The docu¬
mentation is good, answering first¬
time users' questions. It also
gives demonstration programs. But
the part explaining the function of
the rear switches is unclear.
Restated, this 64K RAM always gives
you memory from 16K to 64K. For
normal operation, SW1 is always
off. SW2 turns 8-12K block on or
off. SW3 turns 12-16K on or off.

If all others are off., you must
turn SW4 on. — AZ

16

TEACH KIDS TO COUNT WITH THE ZX81

Some education theorists sug¬
gest that learning to count and
read is enhanced if you create a
large, sharp image in a child's
mind. This image should be easily
recognized and repeated often.

Rapidly moving TV pictures get
credit (and blame) for generating
very powerful attention-grabbing
images that anyone watching learns
quickly. With your ZX81 and some
intelligent program design, your TV
can provide sharp graphic images of
concepts you want to teach.

I wrote this program, COUNT,
to help my three-year-old son learn
to equate a group of objects with a
number. The game draws a random
number of objects on the screen and
asks, "How many?" If he answers
correctly, the computer tells him
he's right and draws another set.

If he's wrong, the computer asks
for another answer.

Since my son can barely count
much less read, written text is
kept to a minimum. To keep things
interesting, the program generates
several shapes that occur randomly.

COUNT fits in a IK machine,
with a little extra room if you
want a fancier win display. Once
you enter the listing and save it,
just tell your child to push R for
RUN. The game repeats until you
pull the plug.

Tom Woods, Jefferson, NH

To enter COUNT, use this guide.
All keys are in graphics mode
(press shift 9 first). — AZ

line 100

shift

Y

shift

T

105

shift

T

shift

Y

200

shift

8

shift

G

shift

5

205

shift

8

shift

F

shift

5

300

shift

R

shift

E

305

shift

Q

shift

W

400

shift

W

shift

W

shift

5

405

shift

E

shift

E

shift

5

500

shift

W

shift

T

505

shift

E

shift

Y

NEW ! ZX81 16K ROM HEW I

BLACK JACK*MflSTER by R. A. Foley
U P t o 7 P 1. a y e r s w i t h " c 3. s i n o ' '
o P t i o n s 1 i k e D o u. b 1 e D o w n , S P 1 i t
P 3. i r s > 8 u. p r e ri cj e r S 1 1 0 u t .. 3. n d
mope! Do’rr't settle Pop less.

FOOTBALL FORECASTER by G. Smith
Get this one QUICK as the data
base is Fop the 82-83 season,,

S P e c i P y C 0 L L E G E o p P R 0 v e p s i o ti ,.
M o ri e y 0 p d e p 9 e t s p u. s h d e l i v e r y .,

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£9606

The words in reverse in lines 45
and 55 are WRONG and RIGHT with
asterisks .

1 LET fi = INT (RNDJ103 +1
5 GOTO 3.00* £ INT (RND*Si +1)

7 FOR X=© TO R-l
10 PRINT RT 9,X*3+l; ft*

IS PRINT RT IS ,X»34l ; BS
a© NEXT X ' ‘

as PRINT RT 0,0; "HOU HRNY?”

3© INPUT D$

35 IF CODE D$>37 OR CODE D*<2S
THEN GOTO 4-5 *

4.0 IF URL D$=R THEN GOTO 55
4.5 PRINT D=£; -

50 GOTO 3© "

J|5 PRINT RT £©,6; "i

100

60 PROSE
65 CLS
70 GOTO 1
10© LET R$ = "V
1©S LET =

110 GOTO 7
20© LET R$=

205 LET B£=

2 10 GOTO 7
30© LET R$="

305 LET B$="

31© GOTO 7
400 LET
4-05 LET B£s
4-1© GOTO 7
50© LET «£ = '•

60S LET B$ = **

51© GOTO 7
SYNTACTIC SUH

354-37 , SK

17

STRING FUNCTION TRANSLATION FOR 8K

While using my 8K ROM and
manual I took up the exercise on
strings that asks you to work out
the equivalents of LEFT$, RIGHT$,
MID$ and TL$. The result is this
demonstration program.

Arthur J. Bumpus, Jr., Brockton, MA

This demo is set up for strings of
more than 7 characters, using 7 as
the variable each time. Try sub¬
stituting other numbers. LEFT$,
RIGHT$, MID$ and TL$ are functions
common to other microcomputers.
These conversions will help you
translate from other BASICS. — AZ

10 REM "STRING FUNCTIONS"

20 REM ZX ee.'SK ROM
•3w Rfc.H hhT BUMPUS
50 REM LEFTS
60 GQ5UB 5@0
7© LET N=7

60 REM PRINTS UP TO 7TH CHRR .
90 LET TO N)

100 PRINT BS; . . LEFTS ,N> " " "

11© REM RIGHTS

is© ggsub see
130 LET N=?

14.0 REM PRINTS FROM 7TH TO END
15© LET BS=RS(N TO )

160 PRINT BS; """RIGHTS ,N)

170 REM MIDS CRS , Nl, N2>

180 GOSUB 50©

190 LET Nl=7
200 LET N2=l
210 LET N3=NI+N2

220 REM PRINTS 1 CHRR. FROM THE
7TH

23© LET BS=RS «:N1 TO N3>

^24-0 PRINT """MIDS ifi$.,Ni,N2> '*

250 REM TLStRS'J
260 GOSUB S©@

27© LET BS=RSC£ TO )

2S0 REM THIS DROPS THE 1ST CHRR

29© PRINT BS; ** "l,TLS 4PS> "" "

300 PRINT "PROGRRM COMPLETED"

310 STOP

500 INPUT FIS

510 PRINT RS;"=“:

520 RETURN

SYNTRCTIC SUM: 334-4-3, 8K

DIAGONAL LINES

You can make 45 degree angles
with two nested FOR-NEXT loops:

1. Diagonal line from lower left
to upper right:

10 FOR A=X TO X where X is lower
left point

20 FOR B=X TO N where N is upper
right point
30 PLOT A,B
40 NEXT A
50 NEXT B

2. Diagonal line from upper left
to lower right:

10 FOR A=X TO X where X is upper
left point

20 FOR B=N TO X STEP -1 where N
is lower right point
30 PLOT A,B
40 NEXT A
50 NEXT B

Here is the listing for "M". Lines
10-30 and 140-160 plot the vertical
uprights .

10 FOR A=10 TO 30
20 PLOT 0 ,A
30 NEXT A
40 FOR B=1 TO 1
50 FOR C=30 TO 24 STEP -1
60 PLOT B,C
70 NEXT B
80 NEXT C
90 FOR D=7 TO 7
100 FOR E=24 TO 30
110 PLOT D,E
120 NEXT D
130 NEXT E
140 FOR F=10 TO 30
150 PLOT 14, F
160 NEXT F

Charles Myler, San Antonio, TX

SHIFTING MAZE— 8K/1K

This program prints a maze on
a IK ZX81. Run in SLOW for best
effect .

10 FOR R=0 TO 19
20 FOR C=0 TO 19
30 PRINT CHR$ ( INT (RND+*5)*2+

3) ;

40 NEXT C
50 PRINT
60 NEXT R

For a shifting maze, add:

5 PRINT AT 0,0;

70 GOTO 5

To exit, press BREAK.

John Burns, Biocal Software,

Fairfax, CA

18

MACHINE CODE PROGRAMMING —
UNDERSTANDING THE STACK

Often when writing machine
code (MC) programs, it's useful to
keep the MC above RAMTOP. But few
people understand how to move
RAMTOP and the Z80's stack pointer
from within MC. The following de¬
tails let you protect your MC pro¬
grams from being overwritten by
using the stack.

In the ZX80/1 with 8K ROM, the
system variable RAMTOP holds the
address of the first location above
usable memory, whether the top of
available RAM or as specified by
the programmer.

The next two bytes, going down
from RAMTOP, are always 3Eh and
OOh. This pair of bytes marks the
top of the GOSUB stack and consti¬
tutes an invalid line number.

Using a RETURN command that fetches
line 3E00 (15872 in decimal) leads
to a "7" error.

Below the top marker of the
GOSUB stack are the return line
numbers of any GOSUB loops that are
active. However, most times a
machine code programmer isn't deal¬
ing with BASIC subroutines; hence
the GOSUB stack will consist of the
top marker alone.

Next comes the point which, in
my manual (p.171) is explained
wrongly — the system variable ERR-
SP, the error stack pointer, points
not to the GOSUB stack but to the
two bytes below it. These two
bytes always hold the BASIC LINE-
RUN return address, 0676h. The
interpreter always returns to this
address after executing subroutines
involved in the interpretation of a
single line.

The normal machine code stack
is below the LINE-RUN return
address .

An important point to note is
that if an error dccurs during part
of the interpretation of a BASIC
line, all the MC stack's details
are discarded as a return is made
to the address held in ERR-SP, ie..

0676h .

Creating a new stack under
programmer's control involves cor¬
rectly placing four bytes — 3Eh,

OOh, 06h and 76h — and giving appro¬
priate values to the stack pointer
and ERR-SP. The following routine
shows one way to do this:

Mnemonic Comment

LD HL,+.... ;your choice for RAMTOP
LD (RAMTOP) ,HL ; enter it
DEC HL ;point to 1st location

LD (HL) ,+3E ;the impossible line #
DEC HL ;point to 2nd location

LD (HL),+00 ;the line #'s low byte
DEC HL ;point to 3rd location

LD (HL),+06 ;return address-high
DEC HL ;point to 4th location

LD (HL),+75 ;low byte of address

INC (HL) ;so as to avoid "76"

LD (ERR-SP) ,HL; this is to be ERR-SP
LD SP,HL ;and the machine code
stack pointer

continue ....

This routine lets you run a
MC program above RAMTOP that will
not be overwritten by use of the
stack. You can make a perfectly
valid RETurn to BASIC if needed.

Note: As I mentioned, when¬
ever an error occurs during the
interpretation of a BASIC line, the
machine code stack is cleared. But
the GOSUB stack is left untouched.
Hence "active" GOSUB return ad¬
dresses remain on the stack, using
up RAM at 2 bytes for each address.

It remains to be seen if this
"bug" occurs in the monitor program
of the ZX Spectrum.

Ian Logan, Skellingthorpe, UK

For further details, see Dr.

Logan's books, Understanding Your
ZX81 ROM and Sinclair ZX81 ROM
Disassembly. Part A and Part B
(with Dr. Frank O'Hara). All three
are available direct from Ian
Logan, 24 Nurses Lane Skelling¬
thorpe, Lincoln LN6 5 'XT, UK, or
from any North American distributor
for Melbourne House Publishing. — AZ

19

SYNTACTIC SUM LOADER

New Readers: Syntactic Sum is a
machine code routine devised by
SYNTAX to help you assure correct
program entry. If two people type
a program exactly the same, they
get the same Syntactic Sum. If one
makes an error, the Sums differ.

The Sum we get when we test each
program appears after the last line
of the published version, along
with the ROM designation. The
following loader program greatly
simplifies using Syntactic Sum for
8K ROM programs. — AZ

This program provides a Syn¬
tactic Sum machine language routine
in just one step instead of the
original multi-step process. Just
LOAD and RUN it, and the Syntactic
Sum program is resident. It also
prints the starting address of the
subroutine for the USR call.

The first part. Listing 1,
consists of a REM statement holding
all the machine code needed to move
the Z80 microprocessor stack and
change all appropriate system vari¬
ables. This has the same effect as
POKEing a new value into the system
variable RAMTOP, then executing a
NEW. The second part POKES a Syn¬
tactic Sum subroutine into the
newly created space at the top of
memory.

To enter this program, follow
these steps:

1. Enter the program in Listing 4.

2. RUN it.

3. INPUT the values in Table 1.
Read them across and press ENTER or
NEWLINE after each. After the last
one, the REM statement in line 1
should have changed to look like
line 1 in Listing 1 following.

4. Enter lines 10-90 of Listing 1,
replacing lines 10-40 of listing 4.

To use this program, type
RUN. ALWAYS RUM THIS PROGRAM IM
TR£ FAST MODE. If- you SAVE it in
FAST, you'll just have to LOAD and
RUN it.

When you run this program, it

returns the number of bytes saved
above RAMTOP and the starting ad¬
dress of the subroutine (INPUT USR
nnnnn). You can access the routine
anytime by entering PRINT USR nnnnn
where nnnnn is the address dis¬
played. The computer does not have
to be in FAST mode to use Listing
1. To clear the Syntactic Sum
loader program from memory before
typing or loading a program, hit
NEW and ENTER or NEWLINE.

This program automatically
calculates locations, so you can
use it with any size memory with no
changes .

You can also use it to load
other subroutines: Put the code
(in hex) in line 10. The first two
characters of A$ are lost in con¬
version, so start your code with
the third character. Change line
50 to TO N+(# of bytes - 1).

Change line 20 to POKE 16507, (num¬
ber of bytes). WARNING — you must
POKE a number greater than 19 or
the computer crashes. You can also
use this program to load more than
one subroutine at a time. Each
time the program is run, the sub¬
routine will be put at the top of
available memory.

This program, together with
other self-loading utilities, is
available on cassette for $4.00.

Roderick McConnell, 28 Orchard St.,

Glen Head, NY 11545

Listing 1

1 REH HE. RND GD5UB 7??*r GOSU
5 ??RND GCSUB ? FOR ; SCSUB f§ GO
SUB 77RNDE, RND GOSUB PIS» RNDE *RN
D GOSUB PX6 *RND GOSUB *?T GOSUB P
X RRND TRN

10 LET R$ = ,‘XXRF4.TS76FE52R0C4.01
17D4-02B4-EE3S3E3ESED52E120F5C1CG”

20 POKE 1650? , 24-

30 PRINT USR IBS 14- ; ’’ BYTES SRU
ED’*

4.0 LET N=PEEK 163S8+2S6SPEEK 1
6389

S© FOR X=N TO N+23

60 LET t 3 TO >

70 POKE X, 16* (CODE +CODE

R$ *2) -28

6© NEXT X

9© PRINT " INPUT USR ** *, N
SYNTACTIC SUM: 1SS3S . 8K

20

LISTING 4

1 REM 12345678901234567890123
456789012345678901234567
10 FOR X=16514 TO 16560
20 INPUT N
30 POKE X,N
40 NEXT X

TABLE 1 — read across

175

42

4

64

237

114

68

77

3

57

237

91

123

64

237

82

235

25

237

184

237

75

123

64

42

4

64

237

66

34

4

64

42

2

64

237

66

34

2

64

237

98

57

237

66

249

201

DICE

ROLL-

•4K/1K

This

program turns

your 4K

ZX80

into

a totally

fair

dice rol-

ler.

It's

a lot quieter

than stan

dard

dice

and

saves

disagreements

about what was actually rolled.

Enter Dice, then RUN (graphics
& spaces are described in PRINT
lines). Hit NL for each roll. To
exit, enter any character.

Lines 40 and 50 roll the dice.
Subroutine 700 arranges the "dots"
on the face of each die. Subrou¬
tine 800 prints the die on the
screen. Who says a IK ZX80 can't
help you play Monopoly!

Robert Masters, Tewksbury, MA

5 LET A$="7space shiftQ 7space"
10 LET B$=CHR$ (130 )

15 LET X$="7space shiftQ"

30 RANDOMISE
40 LET X=RND(6)

50 LET Y =RND ( 6 )

60 LET Z=X
70 GO SUB 700
80 GO SUB 800
90 PRINT
100 LET Z=Y
110 GO SUB 700
120 GO SUB 800
130 INPUT Q$

135 CLS

140 IF Q$=" " THEN GO TO 40
150 STOP

700 LET C$="shiftA 3space shiftA"

701 LET D$=C$

702 LET E$=C$

705 IF Z=1 THEN LET C$="5space"

706 IF Z=1 THEN LET E$=C$

710 IF Z=1 OR Z=3 OR Z=5 THEN L
ET D$="2space shiftA 2space"

720 IF Z=2 OR Z=3 THEN GO SUB 7
50

730 IF Z=2 OR Z=4 THEN LET D$="
5space"

740 RETURN

750 LET C$="shiftA 4space"

760 LET E$=" 4space shiftA"

770 RETURN

800 LET Z$="shif tW"

805 GO SUB 900
810 PRINT A$;B$

820 PRINT X$;C$; "space" ;B$

830 PRINT A$;B$

840 PRINT X$;D$; "space" ;B$

850 PRINT A$;B$

860 PRINT X$;E$; "space" ;B$

870 PRINT A$;B$

875 LET Z$=CHR$ (131)

880 GO SUB 900

890 RETURN

900 PRINT "7space";

910 FOR 1=1 TO 10
920 PRINT Z$;

930 NEXT I
940 PRINT
950 RETURN

SYNTACTIC SUM: -22490, 4K

CARDIOID PLOT— 8K/1K

Cardioid plots a heart-shaped
curve with IK RAM — an attempt to
describe the speed-apparent wind
diagram for a given sail at con¬
stant wind speed. The results can
help predict optimum sailing condi¬
tions .

Frederic D. Bogar, Key West, FL

18 FOR T=PX TO © STEP -.Q5»PZ
50 LET R = f 1+C-OS T) *COS T
60 LET B= C iS*SOR ( (1+COS T)**2
-BBS R**2) )

79 LET X=32+B
©0 LET V =30 — 15 S-R
9© PLOT X,Y
1©0 LET X=32-B
110 PLOT X,Y
12© NEXT T
130 STOP

SYNTRCTIC SUM: 1234-0, ©K

21

CLASSIFIED ADS

***********************************

Use SYNTAX classifieds to sell,
swap or locate ZX products. Rates:
$9 per line. Send your ad, typed
35 char. /line, with check to arrive
by the 15th of any month for next
month's issue. Ads arriving after
the 15th will appear in the issue
following the next month. Repeat
ads must be resubmitted each month.
No phone or credit card orders. We
take no responsibility for classi¬
fied advertisers and have not seen
all products advertised. SYNTAX,

RD 2 Box 457, Harvard, MA 01451.

SYNTAX SUPER DEAL: All back issues,
sub. to Apr83 + binder, $63, call
or write SYNTAX.

Make It Talk - Give It a Good Home
Send SASE for brochure of ZX 80/81
products to KESA Digital, P.O. Box
912 Redmond, OR 97756

ROOMS:1000's of 3D Mazes;9 levels;4
options;send SASE to DEMCo., 211
Nature Trail, Chapel Hill,N.C. 27514

***********************************

* Find out what's available for *
*your computer. The new SINCLAIR *
* COMPUTER FAMILY SOURCEBOOK lists *
*100's of programs , books , & acces- *
*sories from over 70 manufacturers*
*Only $4 . 95+$l . 25 P&H. VA res. add*
*$.20. Send check or MO to Atlantic*

Computer, POB 936 Norfolk, VA 23501*
***********************************

ZX81 2K UPGRADE KIT for 1 or 2 chip
board! All parts, detailed manual.
$2 for your old chips! $15-J Balogh
Box 1319, State College, PA 16801

ZX81 ASSEMBLER & ZX81 DISASSEMBLER
on cassette $15. or for info, send
SASE. Bob Berch 19 Jaques St.
Rochester NY 14620

2 16K games on cass.: Space attack &
Bomber-$6. 5 IK games on cass. $4. 50
Free cat. MILL RESEARCH 2307 Adanac
St .Abbotsford, B.C. CAN. V2S4T1 FUN! ! !

Software & Accessories for the ZX81
Best Prices Anywhere 1 Write for
FREE Catalog: Great Lakes Software

201 Burlington , Valparaiso IN 46383
***********************************

BUFFERED BUSS/DEVELOPMENT BOARD for
ZX80/81 : $40=BARE BOARD, $70=KIT.
UHF modulator $15. Connectors $6.
ZX81 REPAIRS $25. Send for complete
details. COMPUTER CONTINUUM 301-16AV
San Francisco, CA. 94118. (415)5243730

**********************************

! ! ! SUPER SINCLAIR SOFTWARE ! ! !

At last, there is a company which
specializes in programs & games for
TIMEX/SINCLAIR computers w/ 16K RAM
Ask for free catalog from SMARTWARE

PO Box 1491, Melbourne, FL 32935
***********************************

***********************************

A challenging and highly addictive
new video game — LETTER RAIDERS, de¬
veloped by NON-TRIVIAL SOLUTIONS.
The strategy is to capture each
letter of the alphabet on a 24 x 32
grid without recrossing your path.
Also available — LIFE, a simulation
of biological systems, with high
speed 48 x 64 graphics palette.

Both well-documented games are
written in machine language for the
ZX81 with 16K. Order by mail or
phone at $9.95 each from N-TS, P.O.
Box 2941, Amarillo, TX 79105, 806/
376-5723. Check, Visa, MC welcome.
Watch for exciting new developments
coming soon from NON-TRIVIAL
SOLUTIONS!

************************ * (* ********

**ZX81 with 16K RAM FOR SALE**

Used very little. Comes with 2 16K
and one IK cassettes/$130/Call
Laddin after 7PM CDT, 205-974-1501 .

**********************************

FREE SOFTWARE

"Z-WEST" is offering free software
in our ZX-81 users newsletter.

P.O. Box 2411 Vista, Calif. 92083
**********************************

22

ARTIST is a 8K/16K program that,
with more than 25 commands, helps
create drawings/paintings on screen
Features include: user's choice of
brushes and backgrounds, free mix
of graphics and alphanumerics , easy
specification of lines and circles,
ability to store and recreate com¬
plex patterns by defining new
commands, and to save the artwork
on tape or print it. $10. KSOFT ,

845 Wellner, Naperville, Ill 60540

OUR POLICY ON CONTRIBUTED MATERIAL

SYNTAX invites you to express opinions related to any Sinclair computer or
peripheral, or the newsletter. We will print, as space allows, letters discussing items
of general interest. Of course, we reserve the right to edit letters to a suitable length
and to refuse publication of any material.

We welcome program listings for all levels of expertise and written in either
Sinclair BASIC or Z80 machine code. Programs can be for any fun or useful
purpose. We will test run each one before publishing it, but we will not debug
programs; please send only workable listings. Programs submitted on cassette can be
tested more quickly and with less chance of error.

In return for your listing, we will pay you a token fee of $2.00 per program we
use. This payment gives us the nonexclusive right to use that program in any form,
world-wide. This means you can still use it, sell it, or give it away, and so can we.

We will consider submissions of news and hardware or software reviews. Please
keep articles short (350-400 words). Again, we reserve the right to edit accepted
articles to a suitable length. We will pay 7 cents per 6 characters, including spaces
and punctuation, for accepted articles.

When you send in programs for possible publication in SYNTAX, please
include the following information:

• How to operate the program, including what to input if it does not contain
prompts.

• Whether you can run the program over again and how.

• How to exit the program.

• The Syntactic Sum (program published in Feb. 81 and Jun. 81; send SASE
for a free copy).

• What RAM size program requires.

• What ROM program uses.

We pay for this explanatory text at the same rate as for articles in addition to
payment for the program itself.

If you want us to return your original program listing or article, please include
a self-addressed, stamped envelope. Otherwise, we cannot return submitted material.

*KNOW YOUR BIO-RHYTHMS*DISPLAY 12mo
CALENDAR*DI SPLAY lmo CALENDAR .. ZX 81
all three on cassette only $7.95
FREE BIO-RHYTHM FORMS with cassette
send for FREE software catalog and
FREE Hex/Binary/Octal/Dec LISTING
*UAS Box 612 Haddonfield N.J. 08033

LOW LOW LOW LOW LOW LOW LOW LOW LOW

PRICES!

Biorhythms 8K ROM/lK&up . 1.00

Graphics Billboard 8/lup . 1.00

Horse Race 8/lup . 1.00

SPINNER TM (like Rubik 's) 8/16. . .2.00

Improved SLOW PAUSE . 1.00

Linear Regression 8/lup . 2.00

CHAR. Generator Demos 8/lup. . . . 2 . 95

SPLIT-A-STACK TM SLOW/lup . 2.00

CHEWTER TM (like PACMN) SLOW/lup. 2.95

ISLAND SQUARES TM SLOW/2up . 2.00

Random MUSIC! SLOW/lup . 2.00

BASIC Keyword Demos 8/1.... from .50
ORDER, SASE, reSASE gets you GOO¬
DIES Catalog and ! ! FREE ! ! Program
EZRA GROUP II
EZRA GROUP II

POB 5222 San Diego , California 92105

*** SAVE YOUR SUBROUTINES ***

* ADD MEMORY THAT WON'T FORGET! *

* Complete kit: $31:90 incl.s&h *
Full details w/stamp: HUNTER 1630

* Forest Hills, Okemos MI 48864 *

SYNTAX is published

monthly by a wholly-owned
subsidiary of The Harvard Group.

Syntax ZX80, Inc.

RD 2, Box 457, Harvard, MA 01451.

Telephone 617/456-3661.

12 issues, $29. Single issue, $4.

Publisher: Kirtland H. Olson
Editor: Ann L. Zevnik

© Syntax ZX80, Inc., 1981. All
rights reserved. Photocopying
prohibited. ISSN 0273-2696

YES! Please send me 12 issues of SYNTAX for $29.

□ My check for $29 is enclosed. □ Please charge my □ MasterCard
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8 82'

I own a □ Sinclair ZX80 □ Sinclair ZX81 Telephone orders call

617-456-3661

23

SYNTAX

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Plans $3.95 Flashners 7616 Parakeet
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- CHIRPER SOUND FOR ZX81 -

Enter data fast and accurately with
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Sound effects pgm. included. Easy 3
wire hookup. Fits inside ZX81. Send
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BUILD YOUR OWN HARDWARE FOR YOUR
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"UNIVERSAL INVENTORY FILE" You
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Don't write machine code without
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H\R\ARD

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First Class

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PAID

Harvard, MA
Permit No. 8
01451

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************ *